Chapter 8: Q. 37 (page 496)
Abstain from drinking Describe a possible source of error that is not included in the margin of error for the confidence interval in Exercise
There are possible sources of errors.
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The company’s customer satisfaction survey.
In the company’s prior-year survey, 80% of customers surveyed said they were “satisfied” or “very satisfied.” Using this value as a guess for pˆ, find the sample size needed for a margin of error of 3% at a 95% confidence level.
The Gallup Poll interviews people. Of these, say that they jog regularly. The news report adds: "The poll had a margin of error of plus or minus three percentage points at a confidence level." You can safely conclude that
(a) of all Gallup Poll samples like this one give answers withinof the true population value.
(b) the percent of the population who jog is certain to be between .
(c) of the population jog betweenof the time.
(d) we can be confident that the sample proportion is captured by the confidence interval.
(e) if Gallup took many samples,of them would find that of the people in the sample jog.
1. In the company’s prior-year survey, 80% of customers surveyed said they were “satisfied” or “very satisfied.” Using this value as a guess for pˆ, find the sample size needed for a margin of error of 3% at a 95% confidence level.
What if the company president demands 99% confidence instead? Determine how this would affect your answer to Question 1.
Good wood? A lab supply company sells pieces of Douglas fir inches long and inches square for force experiments in science classes. From experience, the strength of these pieces of wood follows a Normal distribution with standard deviation pounds. You want to estimate the mean load needed to pull apart these pieces of wood to within pounds with confidence. How large a sample is needed? Show your work.
- Understand how the margin of error of a confidence interval changes with the sample size and the level of confidence .
AIDS and risk factors In the National AIDS
Behavioral Surveys sample of adult heterosexuals, had both received a blood transfusion and had a sexual partner from a group at high risk of A I D S. We want to estimate the proportion in the population who share these two risk factors.
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